It is known that certain microorganisms, when administered live to humans or to animals, are capable of exerting a beneficial effect on the health of the host, in particular by producing antimicrobial substances.
Such organisms are generally called probiotic organisms.
Numerous studies have shown the beneficial effects, for humans or for animals, of these probiotic organisms, in particular in the treatment of gastrointestinal disorders, such as diarrhoea, acute diarrhoea, and diarrhoea associated with the use of medicinal drugs.
The probiotic organisms most studied to date are the lactic-acid bacteria, but it has also been reported that other live organisms can have a beneficial effect on health.
These other organisms include for example Bacillus subtilis, Bacillus licheniformis, Bacillus coagulans, Bacillus cereus, Bacillus clausii, Bacillus polyfermentans. 
Among these, Bacillus clausii has been used for many years in a pharmaceutical composition marketed under the trade name Enterogermina®.
This pharmaceutical composition is intended in particular for combating gastrointestinal disorders and comprises a mixture of four strains of Bacillus clausii. 
The antimicrobial biological activity of these probiotic organisms is generally linked to the natural production of compounds with antimicrobial activity, such as the lantibiotics. Thus, strains of Bacillus clausii, Streptomyces mutans, Lactococcus lactis produce respectively subtilin, mutacins and nisins, respectively.
Numerous antibiotics are used nowadays as therapeutic substances for the treatment of infectious diseases, but pathogens are becoming more and more resistant to the pharmaceuticals that are used. Some of them are already known to be “multi-resistant” and it is sometimes extremely difficult to treat the infections that they cause.
New molecules having antibiotic properties are therefore constantly being sought.